Due to rapid development of modern technology and enhancement of quality of life, various 3C high-tech electronic products are becoming thinner, lighter, smaller and more versatile. Therefore, various electronic devices are made from semiconductors, such as silicon carbide (SiC) and group III nitrides (e.g., GaN and AlN). In this regard, silicon carbide and group III nitrides display high physical strength, high resistance to corrosion, and excellent electronic properties, such as high hardness of radiation, high breakdown field strength, wide bandgap, high saturated electron drift velocity, and satisfactory high-temperature operability.
Conventional techniques, such as physical vapor transport (PVT) and physical vapor deposition (PVD), are for use in growing crystals from silicon carbide and group III nitrides include as well as mass production of crystals. PVT involves allowing a silicon carbide powder and a group III nitride powder to undergo sublimation in a muffle furnace and driving gaseous silicon carbide and gaseous group III nitrides to a seed crystal by a temperature gradient so as to undergo a crystal growth process. In general, growing silicon carbide crystals by PVT entails: providing a seed crystal; putting the seed crystal in a crucible which comprises a growth chamber, a seed crystal region (inclusive of a holder disposed above the growth chamber, adapted to fix the seed crystal in place, and positioned at the relative cold end of a heat field device for providing the temperature gradient), and a material source region disposed below the growth chamber and adapted to contain a material source; filling the material source region with a carbide raw material so that the carbide raw material undergoes sublimation to become gas molecules; and conveying the gas molecules to a seed crystal wafer to undergo deposition and crystal growth. Applying PVT to growing crystals from silicon carbide and group III nitrides has disadvantages described below. Take silicon carbide as an example, defects of a graphite thermally-conductive layer extend into a wafer. In 1993, Stein discovered a hexagonal vacancy in a silicon carbide wafer produced by PVT and suggested that it results from planar evaporation of the back of the wafer. The nucleation site of the hexagonal vacancy is located at an imperfect point of the graphite thermally-conductive layer between a seed crystal and a seed pad. During the process of crystal growth, the growth of the bottom (near the seed crystal) of the hexagonal vacancy and the evaporation which occurs at the top (near the growth surface) of the hexagonal vacancy together lead to the movement of the hexagonal vacancy. The hexagonal vacancy originates from the imperfect point of the graphite thermally-conductive layer between the seed crystal and the seed pad. The aforesaid phenomenon also causes 6H (or 15R) polycrystalline insertions, carbon-rich depositions, and pyrolysis-related holes. In view of this, the prior art discloses precluding the defects by plating a uniform photoresist layer on the back of the seed crystal to stop silicon carbide from undergoing local sublimation on the back of the seed crystal which might otherwise occur because of the poor heat transfer caused by the holes, but at the expense of the rate of the growth of the wafer and reproducibility.
Since the quality of a wafer produced by PVT depends on the temperature at which the crystal growth process is carried out, the prior art discloses improving a required apparatus to control the growth process temperature. U.S. Pat. No. 5,968,261 discloses forming a cavity in a graphite crucible and applying a thermally insulating material to the inner wall of the cavity to increase the efficiency of the heat dissipation that takes place on the back of a seed crystal. US20060213430 discloses changing the distance between a seed crystal and a holder thereof to control the efficiency of heat transfer between the seed crystal and the holder as well as heat radiation. U.S. Pat. No. 7,351,286 discloses positioning a seed crystal in a manner to reduce the bending of the seed crystal and the effect of a stress thereon. U.S. Pat. No. 7,323,051 discloses positioning a seed crystal by a porous matter disposed on the back of the seed crystal and providing a vapor blocking layer for reducing the sublimation which occurs to the seed crystal. U.S. Pat. No. 7,524,376 provides a thin-walled crucible and discloses growing an aluminum nitride wafer by PVT to reduce a thermal stress. U.S. Pat. No. 8,147,991 discloses controlling the efficiency of heat transfer by adjusting the distance between a seed crystal and a holder thereof.
The aforesaid prior art involves modifying the shape of a crucible or the shape of a seed crystal holder. However, after a growing wafer has attained a large size, the aforesaid prior art fails to dissipate heat sufficiently from the large-sized wafer, further control the shape of the interface of the growth of the wafer, and speed up the growth rate. In view of this, it is important to provide a device adapted for growing monocrystalline crystals and equipped with a heat dissipation component conducive to high efficiency of heat dissipation of large-sized wafers, good balance between process costs and efficiency, and the growth of large-sized monocrystalline crystals by PVT.